SkyWind's rooftop turbine and the IEC 61400-2 standard

The rooftop turbine from Germany's SkyWind NG weighs around 19 kg, has a 1.5-metre rotor and reaches 1,000 watts peak, with certified reference annual output of 615 kWh at an average wind speed of 6 m/s. The publication presents the equipment as a complement to solar generation.

The other side of the asset is missing: design life, replacement interval for bearings and blades, and what remains of the equipment at the end. IEC 61400-2:2013, the international standard for small wind turbines, covers design, installation, maintenance and operation over the planned useful life, and it is this figure that the publication does not provide.

The 615 kWh a year is a reference under favourable wind conditions. On an urban rooftop, with turbulence and obstruction, generation falls, and the equipment has moving parts that a photovoltaic module does not. Without declared useful life and without residual value, the return on micro wind is not comparable with that of solar on the same roof.

Design life and the replacement cost of moving parts decide whether rooftop wind complements the solar system.